Neural feedback loop filters for enhanced dynamic range magnetoencephalography (MEG) systems and methods

Abstract

One embodiment is a magnetic field measurement system that includes at least one magnetometer having a vapor cell, a light source to direct light through the vapor cell, and a detector to receive light directed through the vapor cell; at least one magnetic field generator disposed adjacent the vapor cell; and a feedback circuit coupled to the at least one magnetic field generator and the detector of the at least one magnetometer. The feedback circuit includes at least one feedback loop that includes a first low pass filter with a first cutoff frequency. The feedback circuit is configured to compensate for magnetic field variations having a frequency lower than the first cutoff frequency. The first low pass filter rejects magnetic field variations having a frequency higher than the first cutoff frequency and provides the rejected magnetic field variations for measurement as an output of the feedback circuit.

What is claimed as new and desired to be protected by Letters Patent of the United States is: 
     
       1. A magnetic field measurement system, comprising:
 at least one magnetometer comprising a vapor cell, a light source configured to direct light through the vapor cell, and a detector configured to receive light directed through the vapor cell; 
 at least one magnetic field generator disposed adjacent the vapor cell and configured to modify a magnetic field experienced by the vapor cell; and 
 a feedback circuit coupled to the at least one magnetic field generator and the detector of the at least one magnetometer, wherein the feedback circuit comprises at least two feedback loops, wherein each of the at least two feedback loops comprises a first low pass filter with a first cutoff frequency, wherein each of the at least two feedback loops of the feedback circuit is configured to compensate for magnetic field variations having a frequency lower than the first cutoff frequency using the at least one magnetic field generator, wherein the first low pass filter rejects magnetic field variations having a frequency higher than the first cutoff frequency, wherein each of the at least two feedback loops of the feedback circuit is configured to provide the rejected magnetic field variations for measurement as an output of the feedback circuit. 
 
     
     
       2. The magnetic field measurement system of  claim 1 , wherein the first cutoff frequency is in a range of 5 to 40 Hz. 
     
     
       3. The magnetic field measurement system of  claim 1 , wherein the first cutoff frequency is in a range of 8 to 20 Hz. 
     
     
       4. The magnetic field measurement system of  claim 1 , wherein each of the at least two feedback loops of the feedback circuit comprises a proportional integral derivative (PID) element. 
     
     
       5. The magnetic field measurement system of  claim 4 , wherein the first low pass filter is part of the PID element. 
     
     
       6. The magnetic field measurement system of  claim 1 , wherein the at least one magnetic field generator comprises two pairs of coils, wherein each of the pairs is arranged orthogonal to the other pair and is coupled to a different one of the at least two feedback loops. 
     
     
       7. The magnetic field measurement system of  claim 1 , wherein the feedback circuit comprises three of the feedback loops. 
     
     
       8. The magnetic field measurement system of  claim 7 , wherein the at least one magnetometer further comprises a pump light source configured to illuminate and pump atoms in the vapor cell. 
     
     
       9. The magnetic field measurement system of  claim 7 , wherein the at least one magnetic field generator comprises three pairs of coils, wherein each of the pairs is arranged orthogonal to the other pairs and is coupled to a different one of the three feedback loops. 
     
     
       10. The magnetic field measurement system of  claim 7 , wherein two of the three feedback loops of the feedback circuit further comprise a second low pass filter having a second cutoff frequency, wherein the second cutoff frequency is higher than the first cutoff frequency, wherein the feedback circuit is configured to provide magnetic field variations having a frequency between the first cutoff frequency and the second cutoff frequency as the output of the feedback circuit. 
     
     
       11. The magnetic field measurement system of  claim 10 , wherein two of the three feedback loops of the feedback circuit further comprise a modulation source configured to provide modulation at a modulation frequency to a feedback signal generated by the feedback circuit and delivered to the at least one magnetic field generator, wherein the modulation frequency is greater than the second cutoff frequency. 
     
     
       12. A magnetic field measurement system, comprising:
 at least one magnetometer comprising a vapor cell, a light source configured to direct light through the vapor cell, and a detector configured to receive light directed through the vapor cell; 
 at least one magnetic field generator disposed adjacent the vapor cell and configured to modify a magnetic field experienced by the vapor cell; and 
 a feedback circuit coupled to the at least one magnetic field generator and the detector of the at least one magnetometer, wherein the feedback circuit comprises at least one feedback loop, wherein each of the at least one feedback loop comprises a first low pass filter with a first cutoff frequency, wherein the feedback circuit is configured to compensate for magnetic field variations having a frequency lower than the first cutoff frequency using the at least one magnetic field generator, wherein the first low pass filter rejects magnetic field variations having a frequency higher than the first cutoff frequency, wherein the feedback circuit is configured to provide the rejected magnetic field variations for measurement as an output of the feedback circuit, wherein at least one of the at least one feedback loop of the feedback circuit further comprises a second low pass filter having a second cutoff frequency, wherein the second cutoff frequency is higher than the first cutoff frequency, wherein the feedback circuit is configured to provide magnetic field variations having a frequency between the first cutoff frequency and the second cutoff frequency as the output of the feedback circuit. 
 
     
     
       13. The magnetic field measurement system of  claim 12 , wherein at least one of the at least one feedback loop of the feedback circuit further comprises a modulation source configured to provide modulation at a modulation frequency to a feedback signal generated by the feedback circuit and delivered to the at least one magnetic field generator, wherein the modulation frequency is greater than the second cutoff frequency. 
     
     
       14. The magnetic field measurement system of  claim 12 , wherein the feedback circuit comprises two of the feedback loops. 
     
     
       15. The magnetic field measurement system of  claim 12 , wherein the feedback circuit comprises three of the feedback loops. 
     
     
       16. A magnetic field measurement system, comprising:
 an array of magnetometers, each of the magnetometers comprising a vapor cell, a light source configured to direct light through the vapor cell, and a detector configured to receive light directed through the vapor cell, wherein the array of magnetometers comprises a first magnetometer; 
 at least one magnetic field generator, wherein the vapor cell of each of the magnetometers is disposed adjacent at least one of the at least one magnetic field generator which is configured to modify a magnetic field experienced by the vapor cell; and 
 a feedback circuit coupled to each of the at least one magnetic field generator and the detector of the first magnetometer, wherein the feedback circuit comprises at least two feedback loops, wherein each of the at least two feedback loops comprises a first low pass filter with a first cutoff frequency, wherein each of the at least two feedback loops of the feedback circuit is configured to compensate, in each of the magnetometers, for magnetic field variations having a frequency lower than the first cutoff frequency using the at least one magnetic field generator, wherein the first low pass filter rejects magnetic field variations having a frequency higher than the first cutoff frequency, wherein the feedback circuit is configured to provide the rejected magnetic field variations for measurement as an output of the feedback circuit. 
 
     
     
       17. The magnetic field measurement system of  claim 16 , wherein each of the at least two feedback loops of the feedback circuit comprises a proportional integral derivative (PID) element. 
     
     
       18. The magnetic field measurement system of  claim 17 , wherein the first low pass filter is part of the PID element. 
     
     
       19. The magnetic field measurement system of  claim 16 , wherein at least one of the at least two feedback loops of the feedback circuit further comprises a second low pass filter having a second cutoff frequency, wherein the second cutoff frequency is higher than the first cutoff frequency, wherein the feedback circuit is configured to provide magnetic field variations having a frequency between the first cutoff frequency and the second cutoff frequency as the output of the feedback circuit. 
     
     
       20. The magnetic field measurement system of  claim 16 , wherein the feedback circuit comprises three of the feedback loops.